1. Field of the Invention
The present invention relates to an electrophotographic photoconductor used in a laser beam printer, facsimile machine, digital copier and the like, and to an electrophotographic apparatus and a process cartridge using the electrophotographic photoconductor.
2. Description of the Related Art
Conventionally, various efforts have been made to develop electrophotographic photoconductors utilizing organic photoconductive materials exhibiting outstanding properties in terms of sensitivity, thermal stability, and toxicity and the like for such inorganic materials as Se, CdS, and ZnO, as photoconductive materials used in electrophotographic photoconductors, and electrophotographic photoconductors utilizing organic photoconductive materials are now employed in many copiers and printers. In the case of forming a photo-conductive layer of the electrophotographic photoconductor using the organic photoconductive material, a function-separating type photoconductor in which a charge transporting layer is provided on a charge generating layer is widely used because it excels in sensitivity and durability. In general, in an image forming apparatus such as a printer, copier, or facsimile machine, image formation is carried out by a train series of steps, namely charging step, exposing step, developing step, and transferring step, fixing step. While the high speed and high durability of electrophotographic copiers have advanced in recent years, reliability in a photoconductor to maintain high picture quality even when there is repeated use for an extended period of time is in strong demand. Since copy volume is particularly great in a super high speed copier, stopping the copier many times to replace the photoconductor causes a great reduction of productivity. Further, in a color copier, a tandem system in which four-color development systems are arranged in parallel is widely adopted, and in order to prevent the entire copier from becoming larger in size, use is made of a small-diameter photoconductor in comparison with a conventional one, so additional high durability in a photoconductor is required in response to the high speed of a machine.
Concerning durability, as an abnormal pictures created by the photoconductor, background smear is provided in a current image forming system where negative-positive development is the norm. In the meantime, it is known that it is effective to provide an intermediate layer between a support and a photoconductive layer including a charge generating layer and a charge transporting layer.
For example, Japanese Patent Application Laid-Open (JP-A) No. 47-6341 discloses a cellulose nitrate-base resin intermediate layer; JP-A No. 60-66258 discloses a nylon-base resin intermediate layer; JP-A No. 52-10138 discloses a maleic acid-base resin intermediate layer; and JP-A No. 58-105155 discloses a polyvinyl alcohol resin intermediate layer. However, since these single resin (single layer) intermediate layers have high electric resistance, residual potential is generated, and thus there is picture density reduction in negative-positive development. In addition, because ionic conductivity originated by impurities is indicated, the electric resistance in the intermediate layer becomes especially high at lower temperature and lower humidity, and the residual potential remarkably rises. Consequently, it is necessary for the intermediate layer to be a thin film, with the deficiency that there is an insufficient electrostatic property after repeated use.
In order to solve these problems, as a technology to control the electric resistance of the intermediate layer, the addition of conductive additives to the intermediate layer bulk has been proposed. For example, JP-A No. 51-65942 discloses an intermediate layer formed by dispersing carbon or chalcogen-base substance in a curing resin; JP-A No. 52-82238 discloses a thermal polymer intermediate layer formed by addition of quaternary ammonium salt and by use of an isocyanate-base hardening agent; JP-A No. 55-113045 discloses a resin intermediate layer in which resistance modifier is added; and JP-A No. 58-93062 discloses a resin intermediate layer in which organic metal compound is added. However, these single resin intermediate layers have the problem that a moire image may be generated in a recent image forming apparatus using a coherent light, such as a laser beam.
In addition, for the purpose of simultaneously preventing the moire image and controlling the electric resistance of the intermediate layer, a photoconductor of which the intermediate contains filler has been proposed. For example, JP-A No. 58-58556 discloses a resin intermediate layer in which aluminum or tin oxide is dispersed; JP-A No. 60-111255, a resin intermediate layer in which conductive particles are dispersed; JP-A No. 59-17557 discloses an intermediate layer in which magnetite is dispersed; JP-A No. 60-32054 discloses a resin intermediate layer in which titanium oxide and tin oxide are dispersed; and JP-A Nos. 64-68762, 64-68763, 64-73352, 64-73353, 1-118848 and 1-118849 disclose a resin intermediate layer in which fine particles of boride, nitride, fluoride or oxide of calcium, magnesium or aluminum, are dispersed. For these intermediate layers in which filler is dispersed, in order to present the potential characteristic of the intermediate layer by the dispersed filler, it is necessary to increase the quantity of filler in the intermediate layer, that is, it is necessary to reduce the quantity of resin. Consequently, there is the problem that accompanying the reduction of the amount of resin, adhesion with the support decreases, so peelings between the support and the intermediate layer easily occurs, and in particular, if the support has a flexible belt-like structure, the problem becomes notable.
In order to solve the problem, an approach to provide a laminated intermediate layer has been proposed. The construction of the lamination is roughly divided into two types. One is constructed such that, as shown in FIG. 1, resin layer 303c in which filler is dispersed is provided on the support 301, and then another resin layer 303d which does not contain filler is laminated on the resin layer 303c. Another is constructed such that, as shown in FIG. 2, resin layer 303d which does not contain filler is disposed on the support 301, and the resin layer 303c in which filler is dispersed is laminated on the resin layer 303d. 
Describing the former construction in detail, in order to hide support related defects, a conductive layer in which filler with low resistance is dispersed is provided on the support, on which the resin layer 303d is laminated. Such construction is described, for example, in JP-A Nos. 58-95351, 59-93453, 4-170552, 6-208238, 6-222600, 8-184979, 9-43886, 9-190005 and 9-288367. In such construction, since the conductive layer which is a lower layer essentially fulfills the role of an electrode in the support, the above-mentioned electro-static defects of the photoconductor are still the same as the photoconductor having the single resin intermediate layer. Uniquely, since the conductive layer is composed of a filler dispersed film, scattering of recording light by this layer results in the provision of the moire prevention function. In such construction, because the lower layer is a conductive layer, attaining a charge with opposite polarity to that electrified on the surface of the photoconductor to the interface of the lower layer (conductive layer) and the upper layer (resin intermediate layer) at the time of electrification of the photoconductor results in the realization of the photoconductor action. However, if the resistance of the conductive layer is not so low, the charge injection from the electrode is not sufficiently conducted, and the lower layer becomes a resistance component upon the repeated use, causing a very great rise of the residual potential. In particular, in order to cover defects of the support, which is an objective of this construction, it is essential that the lower layer should be sufficiently thick (10 μm or more), which is a notable problem.
In the meantime, the latter is constructed that the resin single layer having an electron hole blocking function is provided on the support, on which the resin layer in which filler with low resistance or conductive filler is dispersed is provided. Such construction is described, for example, in JP-A Nos. 5-80572 and 6-19174. Since this construction has an electron hole blocking function similar to the former construction, it effectively functions as a background smear. Further, because the filler dispersed film exists on the upper layer; compared to the former construction, the accumulation of the residual potential is lower. In this construction, since the charge (electron hole) injection to the photoconductive layer from the support can be prevented as described above, the background smear phenomenon in the negative-positive development can be considerably reduced. Further, the arrangement of the charge blocking layer to the lower layer also enables the reduction of the rise of the residual potential due to the repeated use, compared to the case of arranging it to the upper layer.
In addition, in JP-A No. 8-44096 discloses an intermediate layer in which the volume content of the contained thermosetting resin is 0.5-0.6 and in which titanium oxide with the provided average particle size is dispersed; JP-A No. 10-301314 discloses an intermediate layer formed by mixing colloid-state alumina into organoalkoxysilane, followed by heating and hardening the mixed composition; JP-A No. 10-90931 discloses an intermediate layer in which thermally-treated titanium oxide is contained in the resin; and JP-A No. 9-34152 discloses an intermediate layer containing a compound selected from metal alkoxide, organic metal chelate, a silane coupling agent and these reaction products on a conductive substrate composed of pure aluminum, aluminum-manganese-base alloy, aluminum-magnesium-base alloy or aluminum-magnesium-silica-base alloy. In any case, the objective is to reduce the background smear phenomenon in negative-positive development by preventing the charge injection from the support to the photoconductive layer.
The resin materials used for these intermediate layers require some functions. The following are provided: (1) in the case of coating a photoconductive layer containing a charge generating layer and a charge transporting layer on the intermediate layer using the wet deposition method, to have the anti-solvent property of not being easily dissolved in a solvent or not for deforming; (2) in order to secure the electric barrier property or not to affect the coating property of the upper layer, to be able to obtain a uniform deposition property without any film defect; and (3) to require excellent adhesion with the support. Consequently, a polyamide-base rein is preferably used as disclosed, for example, in Japanese Patent (JP-B) Nos. 3226110 and 2885609.
However, in general, alcohol soluble polyamide-base resin has a problem, which is the change of the electric resistance according to the use environment. In other words, a photoconductor having the intermediate layer made of alcohol soluble polyamide resin has the problem of great environment dependency, for example, resistance becomes higher and residual potential rises in an environment of lower humidity, and the resistance becomes lower and causes electrification reduction in a environment of high humidity. For this problem, it is known that using polyamide rein, especially N-alkoxymethylated nylon, results in reduced environmental dependency (for example, JP-A Nos. 6-202366 and 63-18185 and Japanese Patent Publication (JP-B) No. 6-93129).
For example, JP-A No. 9-265202 discloses that alkoxymethylated copolymerized nylon with 5 to 30% of degree of alkoxymethylation is contained in an undercoat layer; JP-A No. 2002-107984 discloses that inorganic pigment and N-alkoxymethylated polyamide cross-linked as a binder resin are contained in an intermediate layer; JP-B No. 2718044 discloses that an undercoat layer is composed of N-alkoxymethylated nylon resin, and the element concentrations of impurities, Na and Ca and P atoms, contained in the resin are 10 ppm or less, respectively; JP-B No. 3086965 discloses that N-alkoxymethylated polyamide copolymer in which λ-amino-n-lauric acid is regarded as a main ingredient is contained in an intermediate layer; the above-mentioned JP-B No. 3226110 discloses a method to contain a polyamide resin having a unit component having one structure in an intermediate layer; the above-mentioned JP-A No. 6-202366 discloses an intermediate layer containing an electron-accepting substance along with methoxymethylated nylon; the above-mentioned JP-A No. 63-18185 discloses an intermediate layer containing either N-alkoxymethylated nylon or N-alkylated nylon; and the above-mentioned JP-B No. 6-93129 discloses an intermediate layer containing N-methoxymethylated nylon 6 in which a component(s) whose molecular weight is 1000 or less is contained 10 ppm or less.
In addition to these, in JP-A Nos. 4-170552, 6-208238 and 8-184979, an intermediate layer containing a charge blocking layer containing N-methoxymethylated nylon on a moire preventive layer, which is provided on the support for the purpose of preventing the moire phenomenon due to the interference of a laser beam, is presented.
Although he N-alkoxymethylated nylon is usefully used as a material for an intermediate layer as described above; except for a part of the material, it is dissolved only in an alcohol-based solvent. Consequently, in the case of using the N-alkoxymethylated nylon for an intermediate layer, it is used in a dissolved state in an alcohol-base solvent. However, according to the study by the present inventors, it has been found that there is the great problem that a coating liquid prepared by dissolving the N-alkoxymethylated nylon in an alcohol-base solvent becomes clouded and the viscosity increases (gelated) after storage for an extended period of time or at low temperature. This is not mentioned in detail in the above-mentioned references.
In the meantime, JP-A No. 9-152731 discloses a technology to obtain a long-term storage life by adding halogenated hydrocarbon to an alcohol-base solvent when forming a coating liquid containing alcohol soluble nylon. However, it is not preferable to use halogenated hydrocarbon because of recent environmental problems, so it is difficult to say that this technology can be effectively used, and is a technology that cannot be adopted for actual production.
JP-A No. 2000-56496 discloses a technology to use benzyl alcohol for a coating liquid containing alcohol soluble nylon. This enables extending the life of the coating liquid. However, it has defect that time for drying to touch at the time of coating deposition becomes longer, and thus non-uniformity of film easily occurs. Further, since benzyl alcohol is a solvent having a high boiling point, there is the defect that the drying temperature must be considerably high.
As described above, when coating the coating liquid for an intermediate layer containing N-alkoxymethylated nylon stored for a long term or in an environment of low temperature on the support, non-uniform film thickness or film defects, such as a pinhole, occur, inhibiting the function to block the charge from the support, and abnormal images, such as background smear or black void, are generated. Consequently, the usefulness of N-alkoxymethylated nylon has not yet been effectively utilized.
Further, because the pot life of the coating liquid is short, it is necessary to re-produce it in a short term, with the problem of increased production costs.
As described above, although N-alkoxymethylated nylon is useful as a material for an intermediate layer of the electrophotographic photoconductor, it has the above-mentioned defects, which must be solved.